We report a 5.9-year-old boy with X-linked lymphoproliferative syndrome (XLP) who presented with acute severe infectious mononucleosis. Clinical symptoms rapidly improved after chemotherapy with etoposide. Allogeneic bone marrow transplantation (BMT) was performed after conditioning with etoposide, busulfan and cyclophosphamide. After successful hematopoietic recovery we were able to demonstrate seroconversion from an impaired antibody response to Epstein-Barr virus (EBV) to a normal antibody-producing state in an immunocompetent child. The only post-transplant complication was mild acute graft-versus-host disease (GVHD). Three years after BMT, the boy is healthy and shows no signs of immunodeficiency. This is the first report on successful allogeneic BMT in the severe course of acute infectious mononucleosis in a patient with XLP. We speculate that the application of etoposide contributed to the positive outcome in this patient.